it lwk pisses me off when someone says that something is a run-on sentence just because it’s long, take my previous post for example, obviously it’s not written academically, so i wouldn’t write that in english class, and it might be missing some punctuation (on sigma there’s no way anyone has all 37-or-whatever-the-fuck comma rules memorized), but it’s not a run on sentence; every clause is adequately connected to the rest of the sentence, as is the case in this sentence
an actual run on sentence needn’t be long, it just needs to have multiple clauses that are not connected by a conjunction or a semicolon
and to be clear, they’re completely fine online; not wanting to use full stops and not wanting to seem like the kind of nerd to use semicolons is completely understandable